Solid lead pipes were the norm for hundreds/thousands of years. An oxide patina quickly coats the inside of the pipe and makes it perfectly safe for drinking water. Lead in a faucet is a small problem because the water is not moving, just sitting in the faucet for hours before being needed. You don't have to run the water very long to clear out the little that was in the faucet to have safe drinking water. With the older lead solder in the pipes, you have to run a few gallons to expel what was in the pipes, which doesn't take long. Hot water will cause lead to leach out, but hot water is not usually a concern for drinking. Lead "was" a very important part of plumbing. The word Plumb means lead in Latin I think. Lead makes brass and other metals less expensive, easier to work, and last much longer.
So, why do we think lead in plumbing is so bad? "Someone" in Flint Michigan decided to use a cheaper supply of water for the city. They also decided they didn't need those expensive anti-corrosion or PH modifiers in the new supply of water. The new more caustic supply of water dissolved all the lead oxide patina from the inside of the pipes, then started dissolving the lead itself. But the solid lead pipes that hadn't been a problem in a hundred years took the blame. All of a sudden lead is bad! Blaming the lead pipes takes the focus off what/who really caused the problem, and we are all paying for it. Manufacturers have spent billions redesigning products without lead, and even more money getting "certified lead free and safe". These certifications are mandated by our government officials, the same as the ones who were in control of water quality at Flint. The independent companies the government has picked to do the certifications are raking in the profits. All this cost gets passed right on down to the consumers, who are paying several times more money for plumbing products that last several times less than they should. Switching to plastic just eliminates one of many ways your water quality can still be screwed up by a bureaucracy.
